Enhancing Thermal Energy Storage in a Counterflow Solar Air Heater With Composite Phase Change Materials

ABSTRACT Solar air heaters (SAHs) are constrained in efficiency and operational duration by the intermittency of solar energy. This study addresses these constraints by investigating the use of phase change materials (PCMs) for thermal storage. However, PCMs are hindered by their low thermal conductivity and integration challenges. In this research, a novel double‐fin counterflow SAH was developed using polygonal galvanized iron absorber panels and transverse rectangular fins. The fins were integrated with a phase‐change material composed of paraffin wax and iron filings (2 L of paraffin and 50 g of iron filings). Experiments were conducted in Hawija city, Iraq (35.4586°N, 43.8319°E), over 6 consecutive clear days, evaluating setups with and without PCMs under actual environmental conditions. Key parameters, including efficiency, output temperature, and heat gain, were assessed. The results showed that the inclusion of PCM increased the daily thermal efficiency by 15.2% (from 31.04% to 35.75%), extended heat delivery by 5 h after sunset (until 8:00 p.m. compared to 5:00 p.m. without PCM), and reduced the peak outlet temperature by 7.3% (32.9°C vs. 35.5°C at noon). Furthermore, the average daytime temperature was elevated by 28.8% (18.3°C vs. 14.2°C). This study presents an economical solution for solar thermal stabilization, specifically designed for agricultural drying and building heating in sunny regions. The proposed design addresses PCM conductivity limitations and extends SAH operation beyond daylight hours.